Ram in “Limp” Mode – No power, DTCs P0335, P0642 & P2122 Tech Tips
Details: We found a wiring diagram included with the P0642 DTC diagnosis chart. It seems that all three codes could be set by the sensors connected together in this circuit. We tested the circuit voltage first and verified that the 5-volt reference wire was only showing 1.6 volts. We thought one of the sensors may be shorted so we disconnected all – still read 1.6 volts. Disconnected the 5-volt reference wire connector at the PCM — now we had 5 volts coming out of the PCM. Using the wiring diagram, we found another sensor in the same circuit – the engine oil pressure sensor. Once that sensor was disconnected, we finally got the 5-volt reference back to all sensors.
Confirmed Repair: Once the engine oil pressure sensor was replaced, we cleared codes and retested – all conditions corrected.